Amanda Rivera pointed out that hunters have lost their ability to double, or even triple, trap, and although many hunters were not using this exploit, a large proportion were. Even though this might be a fair fix, I imagine that for many hunters, the raids they have "on farm" will suddenly be much more confusing.
As Robin reported earlier, hunters can no longer use feign death on a boss fight in order to be removed from combat (you can still drop aggro) and go have a drink. Officially, this is a bug fix, and in fact, many hunters had not even realized that they could go take a swig during a boss encounter. Unfortunately, this is not just impacting a Hunter's ability to pump up their mana pool; it's also affecting their ability to feed their pets.
It is being reported that pets are losing happiness at a faster rate post-patch, and that while raiding, because a hunter can no longer feign death and feed their pet, the prospect of using their pet while raiding, or achieving maximum benefit from doing so, is looking somewhat grim for many.
The new pathing changes for pets are also causing serious problems. While a pet on flat terrain will execute attempting to get behind its target without a hitch, any object or elevation that the pet encounters while on its patch has been causing bizarre behavior. The pets are either not attacking when told to do so, or are pacing, often aggroing mobs from the sidelines. In addition, the pathing is causing a reduction in overall DPS, as while the pet is repositioning itself, often very slowly, it is not attacking. While Nethaera has forwarded the information to the devs, it is currently causing a debate about whether hunters want their pets to be attempting this maneuver at all.
In addition to these bugs, the pre-patch question of whether or not hunters will begin to out-level their pets has been answered. Pets do not receive a percentage of gained experience from quests, and because the formula for pet leveling was not altered, hunters are indeed out-leveling their companions. This makes it much more difficult and time-consuming to level a new pet, and considering that pets, and their changeability, are one of the main draws for the entire class, this will hopefully be a very temporary problem.
Fortunately, before the patch, Drysc reported that should a pet leveling issue arise, they have a plan. Let's hope that they can implement it as soon as possible, as all of those leveling hunters taking advantage of the new and improved experience gains are not happy campers.
Considering that many hunters have been very upset with their pets since the advent of the Burning Crusade, it's no wonder that these bugs, in addition to the removal of feign death/drink and double (or triple) trapping, are causing so much commotion.
Update: In response to some of my comments I will say this: Officially, Blizzard is claiming that the ability to double and triple trap was a bug. Using a bug for your own gains is technically an exploit, even if you were not aware that it was indeed a bug. My wording is less a result of me being biased or ignorant, and more my unwillingness to be a conspiracy theorist and claim that Blizzard is lying just so that they could make the change. The fact that this ability was around for so long, and that they are just now noticing it and making changes, does not alter the fact that it remains officially a bug, as fishy as it may seem.